In my U.S. Pat. No. 4,398,994, I have described a continuous method of forming decorative patterns of aluminized plastic film and the use of such patterned film in packaging. As is described therein, a web of aluminized polymer film is printed with a pattern of etchant-resistant material, corresponding to the pattern desired on the aluminized surface. Aqueous sodium hydroxide solution having a concentration of up to about 25 wt. % is applied, at a temperature of about 15.degree. to about 100.degree. C., across the whole width of the web to contact the pattern on the web. The sodium hydroxide solution is allowed to remain in contact with the web as it is conveyed for about 0.1 to about 10 seconds to permit the sodium hydroxide to dissolve aluminum only from areas of the web not having the pattern of etchant-resistant material applied thereto. The spent sodium hydroxide solution is washed from the web to leave the pattern of etchant-resistant material on the transparent polymeric film. The various steps of the operation are effected consecutively at a web speed of up to about 1000 ft/min.
The apparatus illustrated in the aforementioned patent utilizes rollers dipping into baths of liquid to effect the various steps. This manner of application of etchant and of wash water has been found to be somewhat inefficient in ensuring a consistent product at high speeds of operation and also to be uneconomical with respect to utilization of sodium hydroxide etchant.
In an attempt to overcome those difficulties, in my copending U.S. patent application Ser. No. 621,609 filed June 18, 1984, I have described a procedure in which the etchant is spray applied to the film to impinge thereon, scrapers may be used to assist in removal of etched material, warm water sprays wash the spent etchant from the film surface, the washed film is hot air dried and the air-dried film is chilled-roll cooled. By proceeding in this manner, high speed operations may be effected to produce a consistent product with economical use of etchant.
However, the latter operation requires an initial step of applying a pattern of etchant-resistant material to the aluminized surface, the application of an etchant solution over the patterned surface, and the recovery and recycle of etchant solution.
It has also previously been proposed in U.S. Pat. No. 3,647,508 to provide patterns on aluminized plastic film by a procedure which involves printing a pattern of etchant material onto a web of aluminized plastic film using a printing medium comprising a mixture of an etchant, a body-forming member and a volatile carrier. Following printing of the pattern, the volatile carrier is removed to form a spongelike trap for the etchant limiting its spread to the pattern area. Subsequently, the aluminum is washed away to provide the pattern in the etched areas.
Essential to this prior art procedure is the utilization of a volatile carrier for the etchant and some form of heating means to remove the volatile carrier from the etchant. The purpose of the volatile carrier is to enable the pattern to be set and prevent its spread.